This invention relates to the field of automotive engineering, and more particularly to the design of equipment for removing particulate matter from the air drawn into the engines of over-the-road and other vehicles.
In such vehicles, it has been customary to supply air to the engine inlet through a conduit extending rearward from the engine and then upward to an inlet fitting behind and above the cab roof. In this conduit there is connected a filter element, frequently in the form of a hollow member of pleated paper closed at one end so that the air passes through the pores of the paper and particulate matter is retained on the paper surface. Vehicle engines ingest large quantities of air, and in order to reduce the "restriction" or pressure drop in the conduit as far as possible, the latter is made of relatively large diameter. Eight inches is an exemplary diameter for such conduits.
The air cleaners used in such systems became a familiar sight to those using the highways. In diameter they were very comparable with the fuel tank of the vehicle, and for lack of other space they were frequently mounted in an area which could have been used for greater fuel capacity if the fuel tank could have been longer.
Over the years, these air cleaners have been improved by eliminating an initial centrifugal cleaner stage found unnecessary for this service, by using pleated paper cylinders with thinner walls, and by realistic redesigning to set a more appropriate service mileage aim. Each step reduced the physical dimensions of the unit, while maintaining its air flow. It appeared that the limit in improvement by refining mechanical design had been reached. Chemical treatment of the paper offered some room for improvement. One of the principal causes for breakdown of pleated paper filter elements is ingestion of water, and a new inlet fitting which extracts the water by ram action before the air reaches the paper allowed the use of a slightly smaller filter. All these arrangements were designed to be used continuously until accumulation of particulate matter increased the restriction of the filter beyond what was tolerable: the bottom of the housing was then taken off, the element removed and a new element installed.